GB2053357A - Rotary positive-displacement fluid-pressure machines - Google Patents

Abstract

This invention relates to a machine 1 including a casing, having low and high pressure ports 3, 4, intermeshing rotors 5, 6 of toothed form and end plate means 7 having a pressure-balancing arrangement which comprises sealing means separating, one from another, two areas on that face of means 7 remote from the rotors. One of those areas is subjectable to high pressure and the other to low pressure. Flow-restrictive passages 14, 14' are provided in the means 7 which connect with said one area and open onto face 15 at positions 16, 16' closer to port 3 than to port 4 so that pressure fluid fed from said one area through passages 14, 14' is distributed on face 15 in such manner as to cause the positions of the centres of pressure of high and low fluid pressures applied to face 15 to be substantially non-varying during operation of the machine. <IMAGE>

Description

SPECIFICATION Rotary positive-displacement fluid-pressure machines This invention relates to rotary positivedisplacement fluid-pressure machines having intermeshing rotors, for example gear pumps and gear motors.

Hitherto certain such fluid-pressure machines have included an arrangement whereby end plate means provided in association with the rotors of the machines are axially pressure-balanced. Such pressure-balancing has been intended to avoid inadvertent tilting of the end plate means and the onset of consequent premature wear of the rotors and/or end plate means otherwise experienced in machines not so provided with pressure-balancing arrangements.

In order to achieve such pressure-balancing of the end plate means, those end faces thereof remote from the rotors have been so divided by suitably-shaped sealing means as to define areas of the faces which are subjectable to low fluid pressures and areas of the faces which are subjectable to high fluid pressures, the relative sizes of these areas and their disposition being so predetermined that the pressures acting thereupon in operation of the machine do so in opposition to the pressures which subsist in the working spaces of the machine and which are effective upon those faces of the end plate means adjacent the rotors. The pressure-balancing arrangement is intended also to urge the end plate means into adequate sealing engagement with the rotors without the generation of undue friction between the end plate means and the rotors.

In such machines a problem has been found to occur in that variation in the positions of the centres of pressure of both high fluid pressure and also low fluid pressure applied to the faces of end plate means adjacent the rotors has occurred due to variation in the pressure of the fluid, the viscosity of the fluid, and the speed of rotation of the machine. Such variation in the positions of these centres of pressure has been undesirable because, since the positions of the centres of pressure upon the said areas of the respective remote end faces do not vary, the said variation gives rise to undesirable overloading tendency of the end plate means.

In an attempt to overcome this problem, pressure field control grooves have been provided in the face of each end plate means adjacent the rotors, these grooves extending around the face from the high pressure port of the machine each to a predetermined position in the face. However, in operation of the machine it has been found that the high pressure fluid passes from the high pressure port and around the respective pressure field control groove, and leaves the end of the groove remote from that port, at such velocity that it impinges onto surfaces, adjacent that end, of the end plate means and/or casing and/or rotor with such force as to cause undesirable erosion of at least one of these surfaces, depending upon the material thereof. This fluid also has imposed undesirable transient loads on the face in the region of the said end of the groove.Such erosion has been particularly serious with the end plate means where these have been made, for example, from aluminium alloy.

The invention as claimed is intended to provide a remedy. It solves the problem of how to design a rotary positive-displacement fluid-pressure machine having intermeshing rotors in which means are provided for establishing adequate pressure field control on the faces of end plate means adjacent the rotors of the machine but without the disadvantage, experienced with the provision of the above-mentioned pressure-field control grooves, of high velocity impingement of fluid onto said surfaces of the machine.

According to this invention a rotary positivedisplacement fluid-pressure machine includes a casing, having a low pressure port and a high pressure port, at least two intermeshing rotors housed for rotation in said casing, end plate means associated with said rotors, a pressurebalancing arrangement associated with the end face of said end plate means remote from said rotors and with an adjacent face of said casing, said pressure-balancing arrangement comprising sealing means which separate, one from another, a plurality of areas of said end face at least one of which is subjectable to high fluid pressure, and a flow-restrictive passage provided in said end plate means which places said one area in communication with that other face of said end plate means which is disposed adjacent, and which is engaged by, a respective said rotor, the position at which said passage opens to said other face being sufficiently closer to said low pressure port than to said high pressure port that high pressure fluid fed from said one area through said passage to said other face is distributed on said other face in such manner as to cause the positions of the centres of pressure of high fluid pressure and low fluid pressure applied to that face to be substantially non-varying during operation of the machine.

The advantages offered by the invention are that by providing said flow-restrictive passage not only is the high pressure fluid suitably distributed on the respective face of said end plate means adjacent the rotors thereby to cause necessary modification of pressure-balancing as will avoid overloading tendency of the end plate means otherwise due to variation in the pressure of the fluid, the viscosity of the fluid, and the speed of rotation of the machine, but the fluid passes out from the flow-restrictive passage at such a low velocity as to avoid undesirable erosion of any adjacent surfaces upon which it impinges.

One way of carrying out the invention is described in detail below with reference to drawings which illustrate only one specific embodiment, in which: - Figure 1 is a cross-section of a rotary positivedisplacement fluid-pressure machine in the form of a gear pump, Figure 2 is a cross-section taken along the line Il-Il on Figure 1, Figure 3 is a partial and enlarged cross-section taken along the line Ill-Ill on Figure 1, Figure 4 is an enlarged cross-section taken along the line lV-IV on Figure 1, and, Figure 5 is a graphical representation of the pressure distribution on that face portion of end plate means adjacent the upper of the two rotors of the pump, having reference to Figure 4.

The figures show a rotary positivedisplacement fluid-pressure machine 1 in the form of a gear pump intended to draw liquid from a source and to deliver this liquid under pressure to a point of usage. In its basic design the machine includes a casing 2, having a low pressure, inlet, port 3 and a high pressure, outlet, port 4, at least two intermeshing rotors 5, 6 housed for rotation in the casing, end plate means 7 associated with the rotors, and a pressure-balancing arrangement 8 associated with the end face 9 of said end plate means remote from the rotors and with an adjacent face 10 of the casing, the arrangement 8 comprising sealing means 11 which separate, one from another, a plurality of areas 12, 13 of the end face 9 one of which is subjectable to high fluid pressure.

In accordance with the invention a flowrestrictive passage 14, in the form of a drilled hole, is provided in said end plate means 7 which places the one area 12 in communication with that other face 1 5 of the end plate means which is disposed adjacent, and which is engaged by, a respective said rotor 5, 6, the position 16 at which the passage 14 opens to the face 1 5 being sufficiently closer to the low pressure port 3 than to the high pressure port 4 that high pressure fluid fed from the area 12 through the passage 14 to the other face 1 5 is distributed on that face in such manner as to cause the positions of the centres of pressure of high fluid pressure and low fluid pressure applied to that face to be substantially non-varying during operation of the machine.

The rotors 5, 6 each have shafts 17, 18, 19, 20 extending from both sides thereof, the shaft 20 projecting to the exterior of the casing. These shafts are rotatably mounted in respective bushes 21, 23, 24 provided in the casing.

As shown in this embodiment the end plate means 7 is common to the two rotors 5, 6, being apertured at 25, 26 respectively to receive two of the shafts 18, 19 and being generally of figure-ofeight shape to enable it to be housed in overlapping bores 27, 28 provided in the casing 2.

The common end plate means 7 is provided with two of the flow-restrictive passages, the one associated with the rotor 5 being shown at 14 and that associated with the rotor 6 being shown at 14'. The latter passage opens to the face 1 5 at the position 1 6'.

Also in this embodiment two of the common end plate means are provided, one on each side of the rotors, the one associated with the right-hand side of the rotors 5, 6, as viewed in Figure 1, being shown at 7 and that associated with the left-hand side of the rotors being shown at 7'. The means 7' is apertured at 25' and 26'.

In operation of the gear pump above-described the intermeshing toothed rotors 5, 6 draw liquid from a reservoir 29 into the low pressure, inlet, port 3 and discharge this liquid under high pressure by way of the outlet port 4 to a device 30 to be operated by the pump. Hence, as viewed in Figures 2 and 4, the rotor 6 which forms the driven gear is rotated in the clockwise direction, while the rotor 5 which forms the driven or idler gear is rotated in the anti-clockwise direction.

Liquid under high pressure directly derived from the port 4 is applied to the faces 9, 9' of the end plate means 7, 7' over the respective area 12, while the respective area 13, which is separated from the respective area 12 by the sealing means 11, is subjected to liquid at low pressure derived from the port 3. In this embodiment each sealing means 11 comprises a non-extrudable element 31 of plastics material, which is of the generally figure-of-three shape shown in Figure 3 and accommodated in a groove 32 of similar shape, provided in the respective face 9, 9' of the end plate means 7, 7'. A member 33 of rubber is provided under element 31 to provide initial axial bias thereof against the adjacent casing face.

Pressure liquid from area 12 gains access through clearance 34 to member 33 acting thereon to urge element 31 into positive sealing engagement with said casing face.

The pressure distribution on the faces 15, 15' of the end plate means adjacent the rotors 5, 6 is dependent upon the positions 16, 16' of the passages 14, 14' because the latter determine the positions of the centres of pressure of the liquid pressures applied to those faces and thus the effective boundaries between the low pressure and high pressure zones thereon. It will be understood that as each rotor, for example the rotor 5 in Figure 4, rotates, the intertooth spaces 35 successively start to move away from the port 3 and each then contains liquid at low pressure.

Since each intertooth space 35 is exposed to opposite portions of the faces 15, 1 5' of each end plate means, this low pressure is applied to those portions. In Figure 4 positions A, B, C, D, E and F are marked around the upper part of the end plate means 7 corresponding to rotational positions of the teeth 36 of the rotor 5. Figure 5 graphically shows in reiation to those positions on Figure 4 the pressure characteristics of the pump, it being seen that after a tooth 36 has passed the position B, the pressure in the corresponding intertooth space rises steeply to full delivery pressure and is maintained there until that tooth reaches the position F, whereupon the pressure falls off very steeply. Thus, in this embodiment what is termed the "rise point" between low pressure and high pressure in successive tooth spaces occurs between positions B and C. But for the provision of the flow-restrictive passages 14, 14', such a "rise point" would be inconsistent and the said positions of the centres of pressure of both the high liquid pressure and the low liquid pressure applied to the faces 15, 15' would vary with variations in delivery pressure, liquid viscosity and rotational speed of the pump. Such inconsistency would therefore result during operation of the pump in a wide variation of the effective boundaries between the areas at low pressure and the areas at high pressure on the faces 15, 1 5'.

Since the positions of the centres of pressure upon the areas 12 and 13 do not vary, this inconsistency would thus give rise to imperfect balance of the end plate means.

The flow-restrictive passages 14, 14' overcome this imperfection by allowing some high pressure liquid present at the high pressure areas 12 to pass through them to the positions 16, 16' on the faces 15, 15' whereby it is so distributed on those faces in the regions of those positions as to modify the pressure-balancing of the end plate means. In consequence the said "rise point" is maintained substantially consistent, with the said positions of the centres of pressure of the liquid pressures applied to the faces 15, 1 5' being substantially non-varying, this regardless of delivery pressure, liquid viscosity and rotational speed.In such pressure-balancing intertooth spaces 35 containing liquid at high pressure afford high pressure loading of the faces 1 5, 15' in the desired zone in opposition to the high pressure on the areas 12, and the intertooth spaces 35 containing liquid at low pressure afford low pressure loading of the faces 1 5, 1 5' in the desired zone in opposition to the low pressure on the areas 13. This pressure-balancing is such that the end plate means 7, 7' are urged into adequate sealing engagement with the side faces of the rotors without the generation of undue friction, and at the same time the fact that modification of the balancing is afforded by the provision of the restrictive passages 14, 14', results in a substantial reduction, during operation, of overloading of the end plate means. The high pressure area on each face 15, 15' is shown by shading at 37 in Figure 4.

The fact that the flow-restrictive passages 14, 14' afford, by their orificing effect, such improvement in the pressure-balancing of the end plate means irrespective of the pressure of the liquid, the viscosity of the liquid and the speed of rotation of the pump, results in the pump having consistent performance characteristics across wide pressure, temperature and speed ranges.

Further, the passages 14, 14' leading to the positions 16, 16' in the faces 15, 15' are so restricted in their cross-sectional area that they limit the rate of flow of liquid passing therethrough to such a value that liquid discharged at the positions 16, 16' therefrom does so at such reduced velocity that substantially no undesirable erosion of the material of the surfaces of the pump upon which this liquid impinges in the vicinity of the positions 16, 16' takes place.

In this embodiment the toothed rotors 5, 6 are of steel, but the co-operable surfaces of the pump casing and of the end plate means are of a material, such as aluminium alloy, with which erosion would have been a problem due to the higher velocity impingement of liquid thereon in machines where other means, for example grooves disposed in the faces of end plate means adjacent the rotors, are provided for pressure field control on those faces but with no provision for such flow restriction, and where, to overcome the effect of such high velocity impingement, material having high erosion-resistance characteristics would be required. The use of such material would result in a pump which costs more to produce and which is heavier.

Although in the embodiment above-described with reference to the drawings the flow-restrictive passages comprise drilled holes of suitable diameter, in alternative embodiments of the invention these passages may comprise apertures which each incorporate a respective insert, retained therein in convenient manner, having a suitably-calibrated orifice.

Further, although in the embodiment abovedescribed with reference to the drawings the machine is operable as a pump, in other embodiments it may be operable as a motor, in which case the port 4 becomes the inlet port to which liquid derived from a suitable high pressure source is supplied and the port 3 becomes the outlet port which is suitably connected to reservoir.

Again, although in the embodiment abovedescribed with reference to the drawings each of the two end plate means is common to the two rotors, in alternative embodiments each rotor has individual end plate means, one on each side thereof. In this case the end plate means may be of D-shaped cross-section, the two on each side of the rotors thus having flats which are in abutment one with the other, and each being provided with a respective flow-restrictive passage 14, 14'.

Further, in other embodiments the end plate means may be so formed as to provide the entire bushings for the respective rotor shafts.

Finally, although in the embodiment abovedescribed with reference to the drawings the machine is unidirectional in ills operation, in other embodiments the machine, whether a pump or a motor, may be so adapted as to be operable in either direction of rotation of the shaft thereof projecting to the exterior of the casing. To this wend the end plate means on the or each side of the rotors have associated sealing means on the side thereof remote from the rotors which define at least four areas, two of which are in operation always subjectable to high liquid pressures.Of the other two areas one is subjectable to high liquid pressure and the other to low liquid pressure depending upon which of the two ports of the machine forms the inlet port, which of those ports forms the outlet port, and whether the machine is being used as a pump or as a motor. In this case, instead of the face portion of the end plate means adjacent each rotor having one flow-restrictive passage opening to it, it has two such passages, one opening at a position in that face portion which is closer to one of the said two ports and the other opening at a position in that face portion which is closer to the other of said two ports. The distance between said one opening and said one port is equal, or substantially so, to the distance between said other opening and said other port.

Both of said passages are in communication with a respective one of those said areas which in operation are always subjectable to high liquid pressures. Hence, whether the machine is operating as a pump or as a motor, and whether the shaft of the machine projecting from the casing is rotating in one direction or the other, that flow-restrictive passage which opens to said face portion at a position closer to whichever of said ports is at low pressure is the one which affords modification in the pressure distribution in accordance with this invention, thereby to cause the said centres of pressure on the faces of the end plate means adjacent the rotors to be substantially non-varying during operation of the machine, while the other of the two flowrestrictive passages is ineffective in this respect.

Claims (10)

1. A rotary positive-displacement fluid-pressure machine including a casing, having a low pressure port and a high pressure port, at least two intermeshing rotors housed for rotation in said casing, end plate means associated with said rotors, a pressure-balancing arrangement associated with the end face of said end plate means remote from said rotors and with an adjacent face of said casing, said pressurebalancing arrangement comprising sealing means which separate, one from another, a plurality of areas of said end face at least one of which is subjectable to high fluid pressure, and a flow-restrictive passage provided in said end plate means which places said one area in communication with that other face of said end plate means which is disposed adjacent, and which is engaged by, a respective said rotor, the position at which said passage opens to said other face being sufficiently closer to said low pressure port than to said high pressure port that high pressure fluid fed from said one area through said passage to said other face is distributed on said other face in such manner as to cause the positions of the centres of pressure of high fluid pressure and low fluid pressure applied to that face to be substantially non-varying during operation of the machine.

2. A machine as claimed in Claim 1, wherein said rotors each have shafts extending from both sides thereof, one of said shafts projecting to the exterior of said casing.

3. A machine as claimed in Claim 2, wherein said shafts are rotatably mounted in respective bushes provided in said casing.

4. A machine as claimed in either Claim 2 or Claim 3, wherein said end plate means is common to said two intermeshing rotors.

5. A machine as claimed in Claim 4, wherein said common end plate means is apertured to receive two of said shafts and is generally of figure-of-eight shape to enable it to be housed in overlapping bores provided in said casing.

6. A machine as claimed in Claim 5, wherein said common end plate means has two of said flow-restrictive passages, one associated with one of said rotors and the other associated with the other of said rotors.

7. A machine as claimed in any one of Claims 4 to 6, wherein a said end plate means common to said two intermeshing rotors is provided on each side of said rotors.

8. A machine as claimed in any one of the preceding claims, said machine being so adapted as to be operable either as a pump or as a motor.

9. A machine as claimed in any one of the preceding claims, said machine being so adapted as to be operable in either direction of rotation.

10. A machine substantially as hereinbefore described with reference to the accompanying drawings.